Abstract Diabetic Macular Edema (DME) is a vision-threatening stage in Diabetic Retinopathy (DR) that can result in legal blindness. The biochemical mechanisms that drive DME progression are not well understood and treatments address only portions of the disease pathology. The available treatment options vary widely from injectable anti- VEGF to injectable steroids to laser treatments, and carry a heavy cost burden to the US, at over $500 million per year. Currently, there are two large problems with the available treatment options: the efficacy of each treatment is highly variable from patient to patient, and sustained responses are unpredictable. Given the significant increase in diagnoses and the enormous public cost burden, there is a need to develop novel functional biomarker diagnostics which assist physicians in choosing the most effective therapy for each patient. We are developing a companion diagnostic assay for DME which can be used in a clinic setting to allow physicians to predict outcome to anti-VEGF treatment, the first-line of therapy for DME. This assay will enable personalized therapy for each DME patient, by determining appropriate therapy before DME treatment is started, when to switch treatments, and when treatment can be safely stopped (which is currently not possible). Furthermore, as the assay is composed of biomarkers specifically for DME, it can be utilized by pharmaceutical companies for discovery, development, and testing of novel or repurposed drugs for DME. We hypothesize that proteomic analysis of relevant pathways in the vitreous proteome and correlation with clinical symptoms of DME patients receiving anti-VEGF treatment will enable us to develop a predictive biomarker panel for anti-VEGF response in DME. We will use Reverse Phase Protein Microarray assay to detect proteins in vitreous samples collected from DME patients receiving anti-VEGF treatment over time. Targets to be tested include proteins associated with angiogenesis/proliferation, inflammation/ immune response, ischemia/hypoxia and apoptosis/cell survival. Statistical analysis will be performed to examine whether vitreous protein levels are correlated to changes in retinal thickness and visual acuity in response to monthly anti-VEGF treatment. The following specific aims are designed to test our hypothesis and to identify a biomarker panel that predicts treatment response: (1) Identify biochemical pathways involved in changes in retinal thickness and visual acuity in response to anti-VEGF treatment, and (2) Identify a panel of biomarkers that is predictive of changes in retinal thickness and visual acuity in response to anti-VEGF treatment Successful completion of this project will lead to the development of a predictive biomarker panel in the form of a companion diagnostic kit that assists clinicians in determining the most effective therapy for each DME patient. Furthermore, our findings will allow us to collaborate with pharma companies in development of new drug targets.